A single cell energy storage device typically consists of two conducting plates (hereinafter current collectors) and an electronically insulating layer (dielectric, hereinafter separator) disposed therebetween. Electrodes are usually disposed between the current collectors and the separator and a liquid electrolyte (e.g., sulfuric acid) contained therein is used as a charge accumulation interface.
Electrochemical energy storage devices (e.g., primary or secondary batteries, electrochemical cells such as fuel cells) are generally divided into two distinct categories, according to the type of electrolyte used for preparing the electrode, which may be either an aqueous or organic electrolyte solution. The former type may generate up to 1.2 volt per cell, whereas the latter type typically provides about 2.5 to 4.0 volts per cell. The operating voltage of electrochemical energy storage devices may be increased by assembling a plurality of the individual cells described above in series, to obtain an arrangement known in the art as a bipolar cell (e.g., bipolar capacitor).
U.S. Pat. No. 6,212,062 describe the construction of a multi layered capacitor cell wherein carbon electrodes are disposed on the current collectors of the cell.
WO 03/071563 describes an electrochemical energy storage device comprising double layered electrochemical cells and a method for manufacturing the same. In this electrochemical energy storage device, the electrode are printed on the current collectors of the cells and a separating medium is disposed therebetween, wherein the pores of said separating medium in the regions corresponding to the non-printed regions on the current collector (i.e., complementary to the region including the printed electrode) are blocked by a layer of adhesive or other polymer.
According to these methods construction of a bipolar energy storage device consisting from a stack of energy storage cells involves providing electrodes on both sides of each internal current collector in the stack, and one electrode in, contact with the inner face of the two external current collectors (the current collectors placed at the top and the bottom of the stack). This construction is cumbersome due to this electrode arrangement wherein two electrodes are provided on the two sides of each internal current collector of the bipolar energy storage device. Moreover, the sealing and packaging of such cell stacks is not a simple task and the width of their multilayered structure is relatively large.
It is an object of the present invention to provide a simplified multilayered energy storage device construction wherein electrodes may be printed on one side of each current collector.
It is another object of the present invention to provide an improved process for the manufacture of bipolar energy storage devices based on a multi layered stack.
It is a further object of the present invention to provide a method for manufacturing a plurality of energy storage devices stacks wherein an individual energy storage device can be easily cut out by scissors or knife or other mechanical means.
Other objects and advantages of the invention will become apparent as the description proceeds.